[Determination of cholesterol in drainage oil by solid phase extraction-gas chromatography-mass spectrometry]

An effective method was developed for the determination of cholesterol in drainage oil by solid phase extraction-gas chromatography-mass spectrometry (SPE-GC-MS). Firstly, the samples were purified by SPE on a column packed with silica. An extraction yield of 97% was obtained when a 20 mL of ethyl ether/n-hexane mixture (0.6: 99.4, v/v) was used for washing the SPE column, and 10 mL of the same solvent mixture (15: 85, v/v) for desorbing cholesterol from the SPE column. Then the final extract was determined by GC-MS with electron impact ion source. The cholesterol was characterized according to retention time and characteristic fragments (m/z 213, 275, 301, 368, 386), and was quantitatively determined by external standard method in selected ion monitoring mode. The fragment of m/z 386 was selected as the target ion, and m/z 213 and m/z 275 were used as the reference ions. The average recovery was from 91.7% to 101%, and the relative standard deviations (RSDs) were below 6%, and the detection limit was 0.01 mg/L. A good linearity was obtained in the cholesterol concentration range of 0.24 - 6.0 mg/L with the correlation coefficient of 0.999 6. The proposed method can be used to determine the cholesterol content in oil accurately, and the detection result can be one of the criteria judging the existence of drainage oil in edible oil.